(57) A mark having a length nT (n being an integer equal to or greater than 3 and T being
a clock period) is formed by modulating irradiation laser power with three values
of recording power Pw, erase power Pe, and bias power Pb (Pw Pe > Pb). Constant strength
periods of the recording power Pw are set as AtT, AlT, ... , and AmT and constant strength periods of the bias power Pb are set as BtT, BlT, ..., BmT, and CT (C = -1 to 3). The application of laser is divided into pulses in order
of AtT, BtT, AlT, ElT, ... , AmT, BmT, and CT (m = (n-k)/2, k=3 (if n is an odd number), or k=4 (if n is an even number)).
(Here, the constant strength period At of the recording power Pw for n=3, D=4 n≥5 (odd number), and n≥6 (even number) is
set as At3, At4, Atod, and Atev, the constant strength period Bt of the bias power Pb for n=3, n=4, n≥5 (odd number),
and n≥6 (even number) is set as Bt3, Bt4, Btod, and Btev, and then, At3+Bt3 = Atod+Btod = Am+Bm = 2T and At4+Bt4 = Atev+Btev = 3T).
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